During the last decade, heaviest catches have 

 been made south of Oregon within the 5-month 

 period June to October and predominate in small 

 (< 40 pounds), immature fish. 



Sea temperatures greatly influence the 

 distribution of albacore on t h e eastern North 

 Pacific fishing grounds. This influence is char- 

 acterized by seasonal shifts of the entry route 

 into the grounds, and subsequent variation in the 

 patterns of northward movement within the 

 grounds as the season progresses. 



Size distribution also is related to sea 

 temperatures. Small fish abound in tempera- 

 tures of 60 to 65° F. , while larger fish are 

 caught where surface temperatures range from 

 66 to 70° F. 



Small (13 to 20 pounds) albacore are the 

 largest contributors to the eastern Pacific catch 

 while medium to large fish (>20 pounds) are 

 most abundant in the Japanese fisheries. Tre- 

 mendous numbers of youngster s (>10 pounds) re- 

 main undiscovered in the mid-Pacific. 



Clemens, Harold B. 



Migration, age and growth, and spawn- 

 ing studies of the North Pacific alba- 

 core (Thunnus germo). /^Conference 

 Paper II - 2] ( See also Clemens, 

 Harold B. 1961. The migration, age, 

 and growth of I-acific albacore ( Thunnus 

 germo) , 1951-1958. Calif. Dept. of 

 Fish and Game, Fish Bulletin no. 115, 

 128 p. 



This paper presents a brief summary of 

 part of the progress made from 1951 to 1958 by 

 California Department of Fish and Game marine 

 biologists in their study of North Pacific alba- 

 core stocks. Investigations were primarily on 

 albacore interchange between the major North 

 Pacific fishing grounds and changes in fish size, 

 accomplished by making oceanographic and ex- 

 ploratory fishing cruises, studying fishing fleet 

 activities, tagging albacore, and subsequently 

 recovering marked fish from which migratory 

 patterns and growth rates could be interpreted. 



Data from exploratory cruises and fish- 

 ermen's logbooks showed that sea-surface 

 temperature is one of the important factors that 

 influence albacore movements and distribution. 

 The route used by albacore entering the West 

 Coast fishing grounds each season was transient 

 in nature, and its position was regulated prima- 

 rily by sea-surface temperatures between 

 58° and 68° F. After entering the southern 

 California-Baja California fishing grounds, the 

 albacore swing northward upcoast. The route 

 taken in this northward movement also is 

 transient. 



During 15 cruises, 4,585 albacore were 

 tagged and released in the major fishing areas 

 south of San Francisco. There were 73 recover- 

 ies, representing 1.6 percent of the total released. 

 About 80 percent of the tags were recovered with- 

 in the first calendar year of release. Omitting 

 those, 7 percent of the remainder were recovered 

 in the central Pacific, 21 percent off Japan, 62 

 percent in the West Coast fishery the second 

 season, and lOpercent in the West Coast fishery 

 the third season. 



The tagging data confirmed a northward 

 coastal migration as the season progresses. 

 Ninety-five percent of the marked albacore re- 

 captured during their first season at liberty had 

 moved northward from the release point, at an 

 average rate of 6 nautical miles per day (24 

 hours). Summarizing the data by distance. from 

 shore revealedthat albacore traveling within 100 

 miles of the coast averaged about 4 nautical 

 miles daily, while offshore migrants swam al- 

 most 4 times faster. 



A hypothesis on the migratory pattern of 

 albacore was presented. The hypothesis is that 

 albacore from the American fishery (mostly 

 small fish under 20 pounds) cross the ocean in 

 late fall and early winter to enter the area of the 

 Japanese longline fishery, and intermingle with 

 medium-sized fish (20 to 40 pounds) that had 

 moved into the area during the late summer and 

 fall from the Japanese coastal fishery, and with 

 fish of all sizes that had remained in the central 

 Pacific. These fish then move south as the win - 

 ter season progresses. In the spring, the large 

 fish (over 40 pounds) continue south into the 

 North Equatorial Current and Equatorial Coun- 

 tercurrent areas, while the small- and medium- 

 sized fish reverse their course and begin moving 

 north. At this time, some of the fish (medium- 

 sized) travel up the Japanese coast, and some 

 (all sizes) may remain in midocean and travel 

 north and south seasonally. Others (small fish), 

 however, return from the mid-Pacific winter 

 grounds , enter the American fishing grounds, 

 and again travel up the coast and back across the 

 Pacific. 



Albacore growth was estimated fromtag 

 recovery data. Data from 21 tagged albacore 

 that had been at liberty from 9 to 15 months were 

 used to calculate an annual growth curve. The 

 line of best fit for these data is described by the 

 equation Y = 210. 31 + 0. 845 X, and the asymp - 

 totic length attainedby the species is calculated 

 at 135. 6 cm. The results showed that albacore 

 averaging 52 cm. in June (start of the California 

 albacore season) grow to 65 cm. in 1 year, to 

 76 cm. in 2 years, to 85 cm. in 3 years, to93 

 cm. in 4 years, and to 100 cm. in 5 years. It 



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